JPS58108967A - Switching regulator - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Jin's invention relates to a switching regulator, and particularly to a protection circuit against overcurrent.

Conventionally, during daily inspection and maintenance of power supply equipment, the output may be shorted to the ground terminal.
Witehing and Linear Power
Supply D@sign (by th@Hayd
@n Book Company+1977, PP1
83-185).

Overload current may occur during load circuit breakdown or malfunction. Although most overload currents are temporary, it is preferable that the power supply is not affected by them. Due to this precinct, an overcurrent protection circuit is used, and it has been somewhat effective.

The primary purpose of conventional overcurrent protection circuits is to protect the power consumption of linear mode series circuit elements when the output terminal is shorted to ground.

As described above, the main purpose of the conventional safety circuit is to prevent short circuits at the output end of the power supply, but this circuit is also effective against slight overcurrents exceeding the rated maximum load current.

The protection circuit according to the aforementioned document has two operating modes: constant current mode and current holdback mode. In constant current protection mode, when the output current exceeds the rated maximum load current, the output current remains constant. In current holdback mode, the output voltage is kept at a constant value below the rated value until a predetermined current value. When the current value exceeds this predetermined value, the output voltage and output current begin to fold back along the hold pack line.

For linear series regulators, current hold mode is preferable to constant current mode; It cannot be applied directly to the controller.

The conventional overcurrent protection circuit for switching regulators is a modification of the protection circuit for linear regulators, and is based on resetting the core of the switching inductor. This is both expensive and difficult to achieve.
It is.

Furthermore, the switching frequency of a switching regulator (non-clock synchronous) of a hysteresis tight with a conventional overcurrent protection circuit is dependent on the value of the overload resistor. The switching frequency is highest for the critical overload resistor and lowest when shorted, here the critical overload resistor is a resistance slightly lower than the load resistance value that sets the threshold of the overcurrent protection circuit. The high switching frequency obtained with this critical overload resistor is typically higher than the switching frequency of both the transistor switch and the flyback diode, and therefore includes the critical load resistor as well as the short circuit. Highest and constant safe switch for all overload resistance values.

A power source with a proboscis frequency is desired.

Additionally, a power supply with soft start and soft turn-off characteristics is desirable. Soft-start is especially necessary when the load requires very high transient starting currents. Loads that require such a transient high starting current include capacitors/IP capacitors, motors, and incandescent light bulbs.

Soft turn-off is particularly required when unregulated power supplies are turned off. A switching regulator senses the voltage drop and forces more current into the switching transistor to compensate for this. Here, the unregulated power supply is reduced by the slow discharge of the input filter capacitor. As a result, a voltage sufficient to turn on the switching transistor but not to saturate it is applied to the switching transistor. At this time,
Very high currents flow through switching transistors in the active region.

If there is no soft turn-off characteristic, no-date will occur in the switching transistor.

This invention was made to deal with the above-mentioned circumstances,
The purpose is to provide an overcurrent protection circuit for switching levers and regulators with soft start and soft turn-off functions.

According to this invention, the first circuit detects the current flowing through the switching transistor of the switching regulator, and the second circuit supplies a control signal to the circuit that turns off the switching transistor when the current flowing through the switching transistor is equal to or higher than a predetermined value. A circuit is provided.

According to one embodiment of the invention, overload current is detected by a current generator having a transistor biased to detect overload current. This detection means has a resistor, and the voltage across this resistor is input to the overload current detector. The current generated from the overload current detection transistor is an RC whose reference level is the ground level.
Generate voltage in the integrating circuit. This voltage is compared with a reference voltage by an amplitude comparator. The output signal of the amplitude comparator is supplied to the pace drive circuit of the switching transistor of the switching regulator.

Hereinafter, one embodiment of a switching regulator according to the present invention will be described with reference to the drawings. FIG. 1 is a circuit diagram of the first embodiment. The overcurrent protection circuit 10 is shown by a broken line block. A pace drive circuit 14 is connected to the switching transistor Qll. switching transistor Qll
is the unregulated input power supply ML via resistor R12.
and is connected to the output terminal vO via an inductor Lll. Output end vO is connected to a load. 7 Leipa,
The switching transistor Q
ll and the inductor ILI is connected between the connection point of J and the ground terminal.

A voltage sense circuit 16 is connected to the output terminal vO to monitor the output voltage. The output of voltage sense circuit 16 is provided to a hysteretic voltage comparator 18 that drives base drive circuit 14.

The pace drive circuit 14, voltage sense circuit 16, and voltage comparator 18 are shown as fcI diagrams to emphasize that they are common components of switches, chinglegs, and regulators. These details are omitted as they are unnecessary for understanding the invention.

Known examples of these parts include U.S. Pat.
, No. 981 (Bog@), No. 3,772,588 (K@11y @tal), No. 3,931,567
No. (Kost@ek), No. 4,034,280 (C
Ronin et al), Pi' 2 of the above-mentioned book
35-321 mag is now available.

In the overcurrent protection circuit 10, a resistor 812 is connected between the input power supply VL and the emitter of the switching transistor Qll.
is connected. Amplitude comparison transistor Q1 is floating above ground level.

The base of the transistor Ql is a low-pass filter 81 *
It is connected to the output terminal of the switching transistor QJJ via C1. Since the voltage across the resistor 812 is input to the transistor Q1 via the low-pass filters RJ and CJt-, the resistor R12 functions as a current detection resistor.

A resistor R1 is connected between the emitter of the switching transistor Qll and the base of the transistor Q1, and a capacitor C1 is connected between the base and emitter of the transistor Q1. In this way, K, m resistor RJ and canopy arm C1d rotor mother filter are constructed. A low pass filter removes large amplitude signals from the base of transistor Q1.

When the switching transistor Qll is turned on, the current flowing to ground through the diode CRJ1 causes an instantaneous (nanosecond unit) voltage to be applied to the resistor R12.
Occurs between the two ends of . Diode CBII is a 7-star guard diode, but requires a very short recovery time. During this recovery time, diode CRZZ is in conduction mode, conducting current to ground via switching transistor Qll. During the recovery period of the diode CR11, the diode CEL11f current flows as if it were short-circuited. The error filter C1, B1 prevents the recovery current error of these diodes from falsely triggering the overcurrent amplitude detector (current generator) Ql.
Using the elements in the table shown below, the 8
The zero time constant will be approximately 1 μm. In this way, the Ronosfil does not significantly delay the inherent response time of the overcurrent protection circuit 10.

In order to suppress parasitic oscillation when transistor Q1 operates linearly, a resistor R2 is connected to the collector of transistor Q1. Transistor Q1 is a 70-ting overcurrent detector as well as a current generator. Transistor Q1 is off when there is no overload current and is in linear mode when overload current flows through switching transistor Qll. When an overcurrent is detected, the base voltage of transistor Q1 increases linearly, and transistor Q1
becomes the active region. As a result, the collector current of transistor Q1 also increases linearly. Specifically, the collector current flowing through the transistor Q1 is nonlinear outside the collector's cutoff region. However, in practice, the collector current of transistor Q1 can be regarded as a pseudo-linear increasing function.

Capacitor C2 is connected to the collector of transistor Q1, and detects the current from transistor Q1 by comparing it to ground potential. The voltage drop across the capacitor C2 is caused by the converter Ull, resistor R13, FCl4. FCl2.
It is supplied to one input end of a comparator circuit consisting of R16, R17°B18, and a four-capacitor C1l. Resistors RJ5 and RJ
7 sets the threshold value of the comparison circuit. Cano armpit C1
1 is a low-pass filter for minimizing the influence of the two reference level differences (hysteresis) K of the converter u11. The resistor Et14 determines the hysteresis of the resistor υ11, f, tt)-b upper threshold UT and lower threshold LT.Resistor RJj is the resistor RJj
Wir between the output terminal of ll and the input terminal of voltage comparison circuit 180
This is a pull-up resistor for @d-ORf-).

The voltage drop across the capacitor C2 is applied to the converter U11 via a voltage divider consisting of a resistor R16°Rlg. The resistors R16 and RIB also serve as a discharge path for the capacitor C2. As a result, the time constant when the voltage of the canopy capacitor C2 decreases is the product of the parallel resistance value of the resistors R16 and Rlg and the capacitance of the capacitor C2. The capacitor C2 is rapidly charged by integrating the rung current from the transistor fQ1, and is slowly discharged via the resistors R16 and R18.

Canon arm C2 integrates the linear collector runde current from transistor Q1. Comparator Ull is
When the voltage drop across the 4-stage C·S exceeds a steady-state value and reaches the upper threshold UT of the 4-stage regulator Ull, the output is inverted.

When comparator U11 is inverted, Wir@d −OR
A control signal is supplied to the base drive circuit 14 via the base drive circuit 14, and the switching transistor Qll is turned off.

Thereafter, as soon as the canister C1 is discharged by about 0.2 to 0.4V, the transistor Q1 is turned off.

This period is approximately lμs. Transistors Qll and Ql remain turned off until the voltage across capacitor C2 drops to 0°5V (this value is the hysteresis of comparator Ull in the elements in the table below). Capacitor C2
The charging and discharging of Ull and the hysteresis of the converter Ull constitute a relaxation oscillator to set the frequency and duty cycle of the switching regulator under any overload condition.

The waveform that occurs in the capacitor C2 under continuous overload conditions is shown in FIG. Figure 4b shows the output voltage of the comparator Ull.
l starts to fall from the upper threshold UT (3,35V),
Comparator drops. As is clear from FIG. 4b, the comparator drive circuit 14 keeps the switching transistor Qll off. However, when the terminal voltage of the capacitor C2 reaches the lower threshold LT, the output of the capacitor IJ11 becomes a high level signal. , the output of the base drive circuit 14 becomes low level, and the switching transistor Qll is turned on. Here, when transistor QJJ turns on,
If an overload circuit or a short circuit is connected to the output terminal vO, the current flowing through the resistor RJj turns on the transistor Q1 again. As a result, Cano 4 Shita 02 is charged,
The terminal voltage of the canopy arm C2 rises instantaneously at the upper threshold UTt, as shown in FIG. 4a. As a result, comparator UJJ is turned off, the output of base drive circuit 14 becomes high level, and switching transistor QJJ is turned off.

In FIG. 41, the decreasing tendency of the terminal voltage of the terminal C2 of the 14th axis is shown by a broken line. The distance between the upper threshold UT and the lower threshold LT is the hysteresis of the comparator UJJ.

The repetition frequency of the pulse of FIG. 4b is 1 kHz when using the elements shown in the table below. Figures 4a and 4b
In the figure, the starting timing is indicated by a vertical dashed line.

@4b The width Δt of No. 9 and No. 14 Lus shown in figure 4b corresponds to the absolute value of the overload resistance. In case of short circuit, inductor L
Since the reset voltage of ll is the minimum, Δt is the minimum. The typical value of Δt is 5 to 50 (μm), Δt is L
It is expressed as J I X 11/(Vl-VO). Here, Lll is the inductance of the inductor Lll, 11
is the output voltage of transistor Q1, and vl is the unregulated input voltage * 1/1000 Hz)
50 μm, the 1 kHz nominal pulse repetition frequency is almost independent of the absolute value of the overload resistance.

The oscillation frequency of the overcurrent detection consolidator is
The zero frequency number, which can be easily adjusted by changing the capacitance value of C2, is as high as possible, and moreover, the transistor Ql
should be set within the maximum switching frequency of the diode CRII and the maximum switching frequency of the diode CRII. In overcurrent limit mode, the on-duty cycle of switching transistor Qll is very long as shown in Figure 4b. Transistor Ql
In order to keep the switching speed of the switching transistor Q1 and the diode Ca1l below a certain finite value, the switching transistor Q1
The repetition frequency of the ono-no-rusu to 1 is 1000 Hz.
set to the lowest frequency.

The typical switching speed limit value of the transistor Qll and the diode CRJ1 is such that the repetition frequency of the on/off pulse during overcurrent of the transistor Qll is set to about 100 OHs. This repetition frequency is determined by the time constant of the capacitor C2. Minimal overcurrent reversal improves the turn-on characteristics of power supplies for driving incandescent light bulbs, canopies, and motors.

Generally, the overcurrent threshold (IThrs) is expressed as:

VBg (QJoN) 0.6 I? kt・=□Key FCl2 1L12 The overcurrent threshold is preferably set to approximately twice the full load current of the power supply, which is due to the pace emitter voltage VBE(QJO)l) of transistor Q1 when on This is to compensate for changes in resistance tolerance and to prevent false triggering of the overcurrent protection circuit 10.

The current flowing through transistor Qll varies linearly as long as inductor Lll is linear.

The current flowing through transistor Qll continues to change even after overcurrent detection consolidator Ull detects an overload current. In general, the transistor Qll is the transistor Ul
It turns off several μm after l is reversed. This inertial current flows through the switching transistor Qll and the pace drive circuit 1.
4, the faster the switching speed, the smaller it is.

The second embodiment shown in FIG. 2 is a circuit diagram of a current holding circuit including 92 switching transistors Qll and QIJ connected in parallel. The difference from the first embodiment is that in place of the resistor R1 in FIG. 1, resistors R1 and RJ, each of which is about twice as large as R1, are provided. For this,
While the RC time constant is kept at a value determined by the resistor RJ #RJ and the capacitor C3, the input to the transistor Q1 can be made into two paths. Since the transistors Q1 operate in parallel for the same switching input current, the voltage drop during steady-on operation can be reduced to about half.

821! When applying flK I/n, resistors R12 and R20 are 2
There are two functions. The first function is to balance the steady load current between the second function line transistors Qll and QIJ by sensing the load current. Transient low currents cannot be balanced by resistors R12 and R20 because one of transistors Qll and QJJ will switch quickly.
This is because when QJJ turns on, an on-state current of -100 flows through a transistor with a high switching speed.

On the contrary, 100% of the off-state current flows through the transistor having a slow switching speed. Transistor Q11. Q
If the switching speed of 12 is very fast, the time when either one conducts 1001 (theoretically 100 - overload) is very short, so if enough pace drive current is supplied, the transistor Joint (e, tospo,
damage caused by (g) can be avoided.

FIG. 3 shows a third embodiment, which uses a single voltage stabilizing controller--U12. Reducing the number of controllers by one has the effect of saving "DC power" and reducing the overall number of components. In other words, the third embodiment requires less standby power, which provides simplicity and reliability in power conservation. This is effective when applied to space-related equipment that requires high performance.

1% The explanation of the second embodiment is the resistance RJ t of the third embodiment.
This also applies to Rj, canopy C1, and transistor Q1. The canopy starter C101 in series with the canopy starter ClO2 corresponds to the canopy starter 02 in the embodiments of FIGS. 1 and 2. Since the diode CRJ works as a 0R) gate, the voltage sense circuit 16 and the overcurrent protection circuit 10
Either one of them controls the converter UJj.

During normal operation without overload conditions, diode CRJ
is reverse biased, so the overcurrent is passed through the resistor R102,
1 not supplied to the voltage sensing voltage divider consisting of RJ) J
The signal from the voltage divider RJ 02, 810B is
TaUJ,? The $1% signal is input to the reference signal obtained by the resistors R13 to RJF as in the second embodiment.

The output of the converter UJJ is supplied to the base pivot circuit 14 to control the switching transistor Q11ft.

During overload condition, diode CRJ connects to voltage divider R10
2, without passing the signal from R10B, the linear run f signal from transistor Q1 can be passed through canocy CIDI,
Supply to CIO:l. In this, Kagami Konno 9rator U1
2 is inverted, and the switching transistor Qll is turned off. When transistor Qll is turned off, transistor Q1 is also turned off.

Due to the current flowing through the diode CRJ,
The voltage charged to 101aC102 is from the converter/router 11.
When the overvoltage and overcurrent simultaneously exceed the threshold, the current flowing through the diode CRJ no longer charges the capacitors Cl0I and ClO2, however, after half a cycle (approximately 25 μs) the voltage sense The circuit 16 is a switching transistor Qll
Turn it back on. Diode CRJ is a capacitor C
10I, ClO2 is quickly charged and the controller/router U12
is inverted, and the transistor Qll is returned to the off state. That is, diode CRJ is connected to capacitor C101, , C
1O2 is charged exponentially to the hysteresis of the converter/router U12, turning off the transistor Qll within a few μS. Transistor Qll is cano 9sita CJOJ
, CIO:II is kept off until the small voltage that quickly charges it drops. This voltage drop is caused by the resistance R1
Since the signal is passed through the parallel circuit of 02 and R103, it is performed slowly. Cano 9 Shita Cl01. The rapid charging and rapid discharging of ClO2 constitutes a relaxation oscillator. The function of relaxation oscillation is the same as in the first embodiment. The frequency of relaxation excitation is Cano Shita Cl0I.

ClO2 capacitance, resistance R102, R103
is determined by the parallel resistance value of and the hysteresis of the converter U12. Similar to the above embodiment, this frequency is suitably around 1 kHz.

Current protection circuit 10 and voltage sense circuit 16 provide a certain limit on the capacitance of canister C101, ClO2. However, there are compromises where current protection circuit 10 and voltage sense circuit 16 work together well.

Resistance Ω R1100 RJ 100Rj
220R410
k R120,05 RJJ 1.74k RJ4- 115k B15 20.5kR
Jf 28kRJF
20.5k RIB 17.4k RJ9 220820
0.05RIOI
1kRJO264,9
k B103 22.1 Canonomashita F CJ O, 01μ07
0.1μ CJ01 1μ Cl01 1μ C1l 100pie.

Inductor Lll Diode CRJ
lN4150CELII
lN3891 transistor QJ 2N5680Qll
2N6287Qllt
2N6287 Conno Arm Lator UJJ LM139 -'U12
LM139 Although the above description has been made with reference to specific embodiments, the present invention is not limited to these embodiments and can be modified in various ways. For example, a clocked controller may be used instead of a hysteresis controller.

[Brief explanation of drawings]

Figure 1 shows a switching leg according to the invention. The circuit diagrams 1, 2, and 3 of one embodiment of the controller are the circuit diagrams of the 2nd and 3rd embodiments, and the circuit diagrams #44a and 4b are the circuit diagrams of the controller 1111. FIG. 3 is a waveform diagram showing input and output waveforms of U12. 10... Current protection circuit, 14... Pace drive circuit,
16...Voltage detection circuit, 18...Conno 4 regulator,
Qll...Power switching transistor. Applicant's agent Patent attorney Takehiko SuzueFig2゜Fig, 4a. Fig. 4b. IIf

Claims (1)

[Claims] A switching transistor that supplies power to a load connected to an output terminal, a control circuit that controls on and off the switching transistor according to a predetermined input signal, and W that detects the current flowing through the switching transistor.
41 circuit and a second circuit that supplies a signal to the control circuit when the current flowing through the switching transistor is equal to or greater than a predetermined value according to the output of the detector, and when the load is in an overload state, the switching transistor A switching regulator equipped with an overcurrent protection circuit that limits the current flowing through the